Up to now, a large number of sulfonylurea compounds for paddy fields have been in practical use, and used widely and generally as a combined preparation comprising two or more active ingredients with various kinds of Gramineae weed killers effective against weeds of the Gramineae family, but in recent years, there appear weeds resistant to sulfonylurea herbicides such as bensulfuron-methyl, pyrazosulfuron-ethyl and imazosulfuron, and their control becomes problematic.
It is known that weeds resistant to sulfonylurea herbicides are generally cross-resistant to acetolactate synthase (ALS) inhibitors including sulfonylurea herbicides acting on ALS. However, conventional methods for controlling weeds are those methods of adding active ingredients effective against sulfonylurea herbicide-resistant weeds to an existing combined preparation thereby increasing the number of active ingredients in the combined preparation to control the weeds (for example, JP-A 10-287513, JP-A 11-228307 and JP-A 11-349411). Under these circumstances, there is demand for herbicides having a satisfactory effect on weeds resistant to sulfonylurea herbicides and capable of decreasing the number of active ingredients in a combined preparation.